- Email: [email protected]
Arthroplasty in Developmental Dysplasia of the Hip
Arthroplasty in Developmental Dysplasia of the Hip James Cashman, MD, MRCSI, and Kevin J. Mulhall, MD, MCh, FRCSI (TR&Orth) Developmental dysplasia of the hip is a common cause of hip osteoarthritis. Although there have been many advances in surgical techniques of hip joint preservation, once symptomatic degenerative changes are present, arthroplasty or reconstructive procedures remain the main avenues of management. Arthroplasty in this group presents many significant reconstructive challenges in addition to concerns regarding implant survivorship in what is a typically relatively young cohort. In this article we review the many technical aspects of acetabular and femoral reconstruction and the outcomes and potential complications associated with arthroplasty in this group. Despite the complex nature of this surgery, appropriate techniques and implants are associated with excellent symptomatic relief and improved quality of life with acceptable survivorship for these patients. Semin Arthro 19:254-260 © 2008 Elsevier Inc. All rights reserved. KEYWORDS hip, hip dislocation, congenital, arthroplasty, replacement hip
D
evelopmental dysplasia of the hip (DDH) is one of the most common underlying conditions leading to secondary osteoarthritis of the hip. It may be a contributing factor to the development of osteoarthritis in as many as 20 to 40% of patients.1 The natural history of untreated DDH ultimately leads to degenerative joint disease and so there have been many developments in hip joint preservation directed toward altering this natural history. Arguably the most significant development in this regard has been the periacetabular osteotomy originally described by Ganz,2 but joint-preserving approaches continue to evolve with recent evidence pointing toward greater success for these techniques when performed earlier in life. By the time degenerative joint disease is radiologically apparent, however, the opportunity for preventative measures has been lost, and salvage or reconstructive procedures are the only options. Total hip arthroplasty in patients with DDH offers unique reconstructive challenges secondary to deficient acetabular bone stock, abnormal femoral anatomy, limb-length discrepancy, abductor insufficiency, and soft tissue contractures. These patients are also typically younger, placing further demands on prostheses. Both associated abnormal anatomy and patient age have significant implications for surgical approach, implant choice, bearing surface, and long-term implant survival. Department of Orthopaedic Surgery, Mater University Hospital, Dublin, Ireland. Address reprint requests to Dr Kevin J. Mulhall, Suite 4, Sports Surgery Clinic, Santry Demesne, Dublin 9, Ireland. E-mail: [email protected]
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Classification The two most popular classification systems for developmental dysplasia are those of Crowe and Hartofilakidis and coworkers.3-5 They are both useful in surgical planning. The Hartofilakidis classification3 divides dysplasia into three categories: dysplastic hip, low dislocation, and high dislocation. It is our preferred method of classification in assessing the arthritic joint in DDH patients as, in our experience, it relates more directly to basic management decisions for acetabular reconstruction. In a “dysplastic hip” the femoral head is still contained within the original acetabulum but can be associated with segmental deficiency of the superior acetabulum and anterior wall with secondary shallowness due to medial fossa osteophyte. In “low dislocation,” the femoral head articulates in part with the true acetabulum but also with a connected false acetabulum. This type typically presents the most challenging deformities in reconstructive surgery as they are usually associated with the most severe deficiency or even absence of the superior aspect of the acetabulum. There can also be anterior and posterior segmental deficiency and the true acetabulum has a narrow opening and is shallow. With a “high dislocation,” the femoral head has migrated superiorly and posteriorly, having no contact with the true acetabulum. There is circumferential deficiency of this true acetabulum, but it is important to remember that there is often an abnormal distribution of bone stock with relative anterior wall deficiency and relative increased bone stock posteriorly.4 The Crowe and coworkers’5 classification relies on the assumption that the normal ratio of the diameter of the
Dysplasia of the hip femoral head to the height of the pelvis is 1:5 and that any proximal migration of the femoral head can be expressed either as a percentage of the height of the pelvis or of the height of the head–neck junction. It relies on the determination of four landmarks on the anteroposterior radiograph of the whole pelvis. The vertical distance of the femoral head–neck junction from the interteardrop line, which connects the lower part of the radiological teardrops, is defined as the femoral head height. Four types of dislocation of the femoral head (I to IV) are described and, while it is assumed that there is a direct relationship between the severity of the hip disease and the degree of proximal migration of the femoral head, acetabular involvement is not considered.5
Acetabular Reconstruction Anterolateral bone deficiency represents the main challenge in satisfactory reconstruction of the acetabulum. Reconstruction of the dysplastic acetabulum may be accomplished in a variety of ways that are typically predicated on the available bone stock and its distribution. In mild dysplasia it is usually possible to use a small cemented or uncemented socket placed in the native acetabulum at or near the true center of rotation. In more moderate cases, where anterior or superior bone coverage is insufficient, other options include deliberate medialization past the Kohlers line or cotyloplasty (controlled fracture of the medial acetabular wall) to gain improved lateral coverage for the socket (Fig. 1A and B). As the bony deficiency increases, use of a structural bone graft (typically the patient’s own femoral head) becomes the preferred approach. Other options that are described but that we do not employ include implantation in a high hip center posi-
Figure 1 (A and B) Acetabular reconstruction demonstrating medialization of the acetubular component used to gain increase superolateral cover. Note that the collar of the component is not seen in normal profile as it was placed in the extremely anteverted calcar segment.
255 tion (although this approach is definitely not advised for high dislocations) or use of an acetabular reinforcement ring.6 Our preferred approach is to use an uncemented cup at the anatomic hip center whenever possible. Placement of the socket at high hip center positions has several disadvantages, including the necessity for even smaller components, higher risk of impingement (and dislocation), and lack of restoration of limb length and normal hip mechanics. There is also literature to suggest that superior acetabular positioning, even without lateral displacement, leads to increased rates of loosening of both the femoral and acetabular components.7 However, others have found no relationship between the position of the cup and the rate of loosening, while others still have shown that loosening appears to depend on the amount of bony coverage obtained at the time of surgery.8 Although the precise amount of bony coverage required will depend on which acetabular prosthesis is used, most types of uncemented threaded or press-fit sockets have been reported to be successful when 20 or 30% of their surface remained uncovered or covered only with cancellous bone chips.9 In cases in which there is insufficient coverage of the acetabular component, we prefer to use structural autografting, employing the resected head appropriately contoured to create a well-contained acetabulum without excessive overhanging lateral graft. This is fixed in place to the ilium superiorly using a lag screw technique (Fig. 2A and B). Augmentation of an insufficient dysplastic acetabulum with autogenous structural bone graft has several advantages. It more commonly allows the use of a standard size of cup and allows positioning of the cup at or close to the anatomic level. The principle mechanical function of the femoral head autograft is to act as a supporting structure to the socket and to transmit load. If the autograft extends beyond the limit of the acetabular component, some degree of resorption is inevitable, because this part of the graft will not be loaded. Some authors have discouraged the use of bulk structural grafts because of a risk of graft resorption.10 However, Bobak and coworkers11 found that resorption is localized only to the lateral, unstressed part of the graft and that no femoral head graft failures occurred in their series. They reported progressive changes in the graft– host interface up to a mean of 3.5 years and they felt that a minimum of 4 years follow-up was necessary to confirm final graft fixation and incorporation. Hartofilakidis and coworkers12 compared the use of cotyloplasty, in combination with bone grafting and a cemented acetabular component, with a hemispherical cementless acetabular component. They found a significant difference in terms of survival between the two and suggested that the introduction of improved designs with a more stable locking mechanism, the use of highly cross-linked polyethylene, and the potential to use hard-on-hard bearings may lead to longer survival of the cementless components. This latter point is not new and is obviously important as accelerated polyethylene wear, presumably due to increased activity levels, has been held responsible for the higher levels of early failure and rates of osteolysis observed in younger people.13,14 Although the technique of cotyloplasty has not gained widespread use due to concerns
J. Cashman and K.J. Mulhall
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Figure 2 (A and B) Use of femoral head autograft to augment deficient acetabular bone stock in Grade 2 DDH.
about the effect on residual (particularly medial bone stock) and due to results as outlined above, it may still be considered a viable alternative in selected cases.15
Femoral Reconstruction Although there are few detailed studies of the morphology of the dysplastic femur, a thorough knowledge of the altered anatomy in DDH is critical in achieving good results with reconstructive surgery. It is well known that the dysplastic hip is often associated with a narrow medullary canal and increased anteversion.16 The degree of subluxation of the hip also leads to significant alterations in the shape of the femur because of profound changes in the magnitude and direction of the joint reaction force. Since the anatomical abnormalities present are thought to increase with the severity of subluxation of the hip, the technical difficulty in performing joint replacement and the selection of an appropriate femoral prosthesis design can therefore often be related to the severity of the disease. For example, morphological analysis using computerized tomography of the femur in DDH in a Japanese population found that, as the degree of dysplasia and subluxation increases, the hip becomes gradually more anteverted, the neck shorter, and the neck–shaft angle increases.17 Very similar abnormalities have also been found in a European population.18 Similarly, other studies have shown that the dysplastic femur has a straighter, more tapered canal with a narrower medullary isthmus and a more valgus neck– shaft angle than the normal femur.19 When choosing a femoral prosthesis, particular attention must be paid to the stem characteristics, the version of the neck, and the offset so as to adequately restore abductor advantage. Adequate preoperative planning is therefore essential to ensure that appropriate implants are available for the femur in total
hip arthroplasty, a process that is facilitated by the highly modular “stem-in-sleeve” implant types. Abnormal femoral neck anteversion, previous proximal femoral osteotomies, and small femur canals with metaphyseal/diaphyseal mismatch are commonly seen in patients with DDH and are ideal indications for using a modular stem. Modularity optimizes proximal and distal implant stability while permitting adjustments to anteversion, offset, and leg length to provide custom biomechanical reconstruction of the DDH hip. Good clinical results with few complications have been reported with the use of this type of stem in complex DDH surgery.20 In cases of high dislocation, returning the center of rotation to the anatomic hip center will be accompanied by limb lengthening (Fig. 3A and B). When this is predicted to be at or greater than 3 cm it is wise to plan for a shortening osteotomy to avoid overlengthening with resultant excess tension on the neurovascular structures and the femoral and sciatic nerves in particular. Different techniques are described, but our preferred approach is to perform a subtrochanteric osteotomy. We prepare the metaphyseal segment first for the appropriately sized modular collar or sleeve and prepare the canal for a well-fitting stem. The osteotomy then is performed and the length of the appropriate shortening segment is determined by reducing the proximal fragment, with trial implants in place, and directly measuring the length of femur that needs to be resected to get a stable appropriate length construct. With a well-fitting stem the torsional stability of the fluted modular stem gives excellent fixation of the subtrochanteric osteotomy alone, but we often supplement the osteotomy site with a strut derived from the resected femur (Fig. 3C). Although modular constructs have gained increasing popularity for these complex reconstructions there are a wide variety of implants that have been and continue to be used.
Dysplasia of the hip
257
Figure 3 (A-C) Anteroposterior radiograph and computed tomography reconstruction views of High/Grade 3 dislocation, demonstrating pseudoacetabulum in typical posterosuperior location. A subtrochanteric osteotomy allows restoration of the anatomical hip center in the true acetabulum without excessive leg lengthening. A strut of resected femur was replanted with cerclage cables at the osteotomy site. Because of extremely small true acetabular dimensions it was decided to use a cemented highly cross-linked polyethylene cup and obtain maximum polyethylene thickness rather than our standard approach of using an uncemented cup.
Reconstructing appropriate version limits the usefulness of many metaphyseal fixed uncemented components in moderate or severe cases in which the native femur is very anteverted. Cemented components can avoid this drawback by allowing a downsized stem to be placed in the correct version. Resurfacing arthroplasty has gained popularity worldwide and has been described for use in DDH. One of the continued advantages of resurfacing is the preservation of femoral bone stock for future possible revisions; however, other previous potential advantages of hard and large diameter bearings are increasingly also offered by other modular uncemented implants. The Birmingham resurfacing implant has a specific “dysplasia” cup that allows supplementary screw fixation if deemed necessary and medium-term results with this implant in all grades of developmental dysplasia have been acceptable, albeit worse than in matched patients with osteoarthritis treated in the same manner. McBryde and coworkers21 found a significant difference in survival, with 5.2% of patients with dysplasia requiring revision compared with 0% of those with osteoarthritis. However, there was no difference in Oxford hip score between those two groups. Other studies have also reported inferior results for resurfacing in DDH in comparison with patients with other condi-
tions, with, notably, acetabular failures being more prevalent than failures on the femoral side.22
Outcomes of Total Hip Arthroplasty in DDH The use of bulk structural autologous graft from the femoral head to augment the superolateral aspect of the acetabular rim was initially proposed by Harris.23 Although the shortterm clinical results of this technique were excellent, the failure rate after approximately 12 years was high (46%). This may be related to the complex pathoanatomy encountered at the level of the true acetabulum and the abnormal distribution of stresses combined with the unfavourable long-term biological behavior of structural grafts.24 Others have demonstrated a 20% revision rate and a 46% rate of radiological failure at a mean follow-up of 11.8 years.10 However, descriptions of THA for Grade 2 or 3 DDH without the use of autograft have been very poor, with rates of failure between 16 and 59% after follow up for 8.5 to 16 years.8 Various authors have reported on the use of total hip arthroplasty in younger patients. Kim and coworkers25 re-
J. Cashman and K.J. Mulhall
258 ported on 10-year follow-up of cementless prostheses in patients less than 50 years of age. They found a survival rate of 99%, with no case occurring because of aseptic loosening. They reported a thigh pain rate of 10%, with all resolving by 2 years. Dudkiewicz and coworkers26 showed poorer survival in patients less than 30 years with predominately cementless implants. This small series had a revision for any reason rate of almost 50%. One group found excellent clinical results with Charnley low friction arthroplasty with up to 15 years follow-up. They emphasized preoperative assessment, adequate exposure, availability and selection of instruments and components, correct placement of components, and attention to detail at every stage are the most important aspects of the procedure.11 In a series of Birmingham hip resurfacings it was found that younger patients had a significantly worse outcome in terms of Oxford hip score and slightly worse survival than older patients, with the authors claiming this was due to secondary causes of osteoarthritis such as DDH, which represented 10% of their study population.27 The medium-term clinical results of other surface arthroplasties in patients with Crow type I or II DDH have also failed to meet initial expectations, with a 10% conversion rate to total hip arthroplasty due to impingement, femoral component loosening, or femoral neck fracture.28 The risk factors for femoral neck fracture in hip resurfacing for developmental dysplasia, as determined by retrieval studies, included poor bone quality with large cysts and inadequate component seating.29
Complications and Revision Most of the complications typically associated with arthroplasty in DDH are related to the degree of abnormal anatomy. Patients with unilateral high dislocations have substantial limb-length discrepancies and limps. Recent clinical studies have shown excellent results when good primary stability is achieved and the joint is restored to the anatomic hip center.30 However, restoring the normal hip center is complicated by not just bone stock issues but also soft tissue contractures. The rate of nerve palsies is higher after total hip arthroplasty in patients with hip dysplasia, and this has been commonly attributed to stretching of the nerves during lengthening.31 The exact amount of distraction that will cause sciatic nerve dysfunction is not known, but acute lengthening of ⬎2 to 4 cm has been associated with an increased risk of nerve injury.32 However, in a 1999 report on eight nerve palsies after 508 total hip arthroplasties, Eggli and coworkers33 indicated that the palsies were not related to the amount of lengthening per se but to the difficulty of the surgery. There were no clinically evident femoral or sciatic nerve palsies in one series of patients with Crowe IV dysplasia treated with total hip arthroplasty.34 As mentioned earlier, if we predict 3 cm or greater lengthening, our preferred method of controlling length is by a subtrochanteric osteotomy. In our experience this has not been associated with any complications but there is the possibility of delayed or nonunion at the osteotomy site.
Figure 4 (A-C) A patient with cerebral palsy and spastic diplegia with progressive subluxation despite osteotomies of femur and pelvis. Because of intrinsic stability issues in this patient a constrained acetabular implant was employed.
Dysplasia of the hip The rate of dislocation after total hip arthroplasty in these cases has been reported to be as high as 5 to 11%. This is related to the complexities of femoral and acetabular version, soft tissue tension, length, and small component size and emphasizes the importance of a sound knowledge of the individual anatomy in placing components accurately and of performing meticulous intraoperative assessment of stability (Fig. 4A and B). As most of these patients are younger and more active, the main long-term issues remain wear, osteolysis, and failure. There have been many developments in bearings and materials in recent times and it is hoped these will improve implant survivorship for these patients. There are ongoing concerns regarding metal-on-metal bearings in all patient groups, but particularly in women of child-bearing age because of concerns that associated ion levels may cause birth defects. Although there is no clinical evidence demonstrating an increased incidence of cancer or birth defects with metalon-metal bearings, many surgeons are using highly crosslinked polyethylene with larger diameter heads or ceramic bearings in these patients with good results to date compared with traditional polyethylene bearings.13,35-37 Revision total hip arthroplasty in patients with a previous diagnosis of DDH can also be a challenging and technically demanding procedure. Two major concerns are deficient acetabular bone stock and the position of the acetabular implant, particularly if the center of the hip has not been restored in the primary procedure. While some advocate the use of a high hip center to take advantage of remaining bone stock and to avoid the use of a structural graft,38 this does not contribute to the correction of limb-length discrepancy, does not provide good bone stock for revision surgery, and is associated with early acetabular loosening and a higher rate of ischial impingement.7 The pattern of bone loss in DDH, a reduced anteroposterior diameter combined with poor superior support, may be further increased by surgical bone loss from the primary operation, migration of the cup, and particle-induced osteolysis. Anatomical placement of the acetabular component should be the goal in revision THA. However, it is sometimes impossible to achieve adequate contact between the host one and the implant because of severe and progressive bone destruction after the primary procedure. Such bone loss can be managed by the use of structural allograft bone, by impaction grafting over suitably fixed mesh and a cemented cup, by proximal placement of the cup, or by using uncemented implants such as oblong, trabecular metal or jumbo cups or customized implants.39,40 The choice of approach here obviously depends to an extent on availability and experience, but it is worth noting that high cup placement in revision surgery in these cases has been associated with loosening of the acetabular component in 41% at 2 and 5 years.
Conclusion In summary, patients with DDH present a unique set of reconstructive problems based on abnormal femoral and acetabular anatomy. They also develop degenerative joint dis-
259 ease requiring arthroplasty at a relatively young age with associated implications for outcomes and implant survivorship. Despite these considerations, once appropriate techniques and implants are used, there is good evidence to show excellent symptomatic relief and improved quality of life with acceptable survivorship after total hip arthroplasty for DDH.
References 1. Mavcic B, Iglic A, Kralj-Iglic V, et al: Cumulative hip contact stress predicts osteoarthritis in DDH. Clin Orthop Relat Res 466:884-891, 2008 2. Kim YJ, Ganz R, Murphy SB, et al: Hip joint-preserving surgery: Beyond the classic osteotomy. Instr Course Lect 55:145-158, 2006 3. Hartofilakidis G, Stamos K, Ioannidis TT: Low friction arthroplasty for old untreated congenital dislocation of the hip. J Bone Joint Surg Br 70:182-186, 1988 4. Hartofilakidis G, Stamos K, Karachalios T, et al: Congenital hip disease in adults: Classification of acetabular deficiencies and operative treatment with acetabuloplasty combined with total hip arthroplasty. J Bone Joint Surg Am 78:683-692, 1996 5. Crowe JF, Mani VJ, Ranawat CS: Total hip replacement in congenital dislocation and dysplasia of the hip. J Bone Joint Surg Am 61:15-23, 1979 6. Kobayashi S, Saito N, Nawata M, et al: Total hip arthroplasty with bulk femoral head autograft for acetabular reconstruction in developmental dysplasia of the hip. J Bone Joint Surg Am 85:615-621, 2003 7. Pagnano W, Hanssen AD, Lewallen DG, et al: The effect of superior placement of the acetabular component on the rate of loosening after total hip arthroplasty. J Bone Joint Surg Am 78:1004-1014, 1996 8. MacKenzie JR, Kelley SS, Johnston RC: Total hip replacement for coxarthrosis secondary to congenital dysplasia and dislocation of the hip: Long-term results. J Bone Joint Surg Am 78:55-61, 1996 9. Dorr LD, Tawakkol S, Moorthy M, et al: Medial protrusio technique for placement of a porous-coated, hemispherical acetabular component without cement in a total hip arthroplasty in patients who have acetabular dysplasia. J Bone Joint Surg Am 81:83-92, 1999 10. Mulroy RD Jr, Harris WH: Failure of acetabular autogenous grafts in total hip arthroplasty: Increasing incidence. A follow-up note. J Bone Joint Surg Am 72:1536-1540, 1990 11. Bobak P, Wroblewski BM, Siney PD, et al: Charnley low-friction arthroplasty with an autograft of the femoral head for developmental dysplasia of the hip: The 10- to 15-year results. J Bone Joint Surg Br 82:508511, 2000 12. Hartofilakidis G, Georgiades G, Babis GC, et al: Evaluation of two surgical techniques for acetabular reconstruction in total hip replacement for congenital hip disease: Results after a minimum ten-year follow-up. J Bone Joint Surg Br 90:724-730, 2008 13. Torchia ME, Klassen RA, Bianco AJ: Total hip arthroplasty with cement in patients less than twenty years old: Long-term results. J Bone Joint Surg Am 78:995-1003, 1996 14. Devane PA, Robinson EJ, Bourne RB, et al: Measurement of polyethylene wear in acetabular components inserted with and without cement: A randomized trial. J Bone Joint Surg Am 79:682-689, 1997 15. Hartofilakidis G, Karachalios T: Total hip arthroplasty for congenital hip disease. J Bone Joint Surg Am 86:242-250, 2004 16. Charnley J, Feagin JA: Low-friction arthroplasty in congenital subluxation of the hip. Clin Orthop Relat Res 91:98-113, 1973 17. Sugano N, Noble PC, Kamaric E, et al: The morphology of the femur in developmental dysplasia of the hip. J Bone Joint Surg Br 80:711-719, 1998 18. Argenson JN, Ryembault E, Flecher X, et al: Three-dimensional anatomy of the hip in osteoarthritis after developmental dysplasia. J Bone Joint Surg Br 87:1192-1196, 2005 19. Paavilainen T, Hoikka V, Paavolainen P: Cementless total hip arthroplasty for congenitally dislocated or dysplastic hips: Technique for replacement with a straight femoral component. Clin Orthop Relat Res 297:71-81, 1993 20. Mattingly DA: The S-rOM modular femoral stem in dysplasia of the hip. Orthopedics 28:s1069-1073, 2005
260 21. McBryde CW, Shears E, O’Hara JN, et al: Metal-on-metal hip resurfacing in developmental dysplasia: A case-control study. J Bone Joint Surg Br 90:708-714, 2008 22. Davlin LB, Amstutz HC, Tooke SM, et al: Treatment of osteoarthrosis secondary to congenital dislocation of the hip: Primary cemented surface replacement compared with conventional total hip replacement. J Bone Joint Surg Am 72:1035-1042, 1990 23. Harris WH, Crothers O, Oh I: Total hip replacement and femoral-head bone-grafting for severe acetabular deficiency in adults. J Bone Joint Surg Am 59:752-759, 1977 24. Goldberg VM: The biology of bone grafts. Orthopedics 26:923-924, 2003 25. Kim YH, Oh SH, Kim JS: Primary total hip arthroplasty with a secondgeneration cementless total hip prosthesis in patients younger than fifty years of age. J Bone Joint Surg Am 85:109-114, 2003 26. Dudkiewicz I, Salai M, Ganel A, et al: Total hip arthroplasty in patients younger than 30 years of age following developmental dysplasia of hip (DDH) in infancy. Arch Orthop Trauma Surg 122:139-142, 2002 27. Steffen RT, Pandit HP, Palan J, et al: The five-year results of the Birmingham Hip Resurfacing arthroplasty: An independent series. J Bone Joint Surg Br 90:436-441, 2008 28. Amstutz HC, Antoniades JT, Le Duff MJ: Results of metal-on-metal hybrid hip resurfacing for Crowe type-I and II developmental dysplasia. J Bone Joint Surg Am 89:339-346, 2007 29. Amstutz HC, Campbell PA, Le Duff MJ: Fracture of the neck of the femur after surface arthroplasty of the hip. J Bone Joint Surg Am 86: 1874-1877, 2004 30. Perka C, Fischer U, Taylor WR, et al: Developmental hip dysplasia treated with total hip arthroplasty with a straight stem and a threaded cup. J Bone Joint Surg Am 86:312-319, 2004
J. Cashman and K.J. Mulhall 31. Schmalzried TP, Amstutz HC, Dorey FJ: Nerve palsy associated with total hip replacement: Risk factors and prognosis. J Bone Joint Surg Am 73:1074-1080, 1991 32. Lewallen DG: Neurovascular injury associated with hip arthroplasty. Instr Course Lect 47:275-283, 1998 33. Eggli S, Hankemayer S, Muller ME: Nerve palsy after leg lengthening in total replacement arthroplasty for developmental dysplasia of the hip. J Bone Joint Surg Br 81:843-845, 1999 34. Lai KA, Shen WJ, Huang LW, et al: Cementless total hip arthroplasty and limb-length equalization in patients with unilateral Crowe type-IV hip dislocation. J Bone Joint Surg Am 87:339-345, 2005 35. Brodner W, Grohs JG, Bancher-Todesca D, et al: Does the placenta inhibit the passage of chromium and cobalt after metal-on-metal total hip arthroplasty? J Arthroplasty 19:102-106, 2004 36. Bizot P, Hannouche D, Nizard R, et al: Hybrid alumina total hip arthroplasty using a press-fit metal-backed socket in patients younger than 55 years: A six- to 11-year evaluation. J Bone Joint Surg Br 86:190-194, 2004 37. Riska EB: Ceramic endoprosthesis in total hip arthroplasty. Clin Orthop Relat Res 297:87-94, 1993 38. Russotti GM, Harris WH: Proximal placement of the acetabular component in total hip arthroplasty: A long-term follow-up study. J Bone Joint Surg Am 73:587-592, 1991 39. Tanzer M: Role and results of the high hip center. Orthop Clin North Am 29:241-247, 1998 40. Perka C, Schneider F, Labs K: Revision acetabular arthroplasty using a pedestal cup in patients with previous congenital dislocation of the hip: Four case reports and review of treatment. Arch Orthop Trauma Surg 122:237-240, 2002
D
evelopmental dysplasia of the hip (DDH) is one of the most common underlying conditions leading to secondary osteoarthritis of the hip. It may be a contributing factor to the development of osteoarthritis in as many as 20 to 40% of patients.1 The natural history of untreated DDH ultimately leads to degenerative joint disease and so there have been many developments in hip joint preservation directed toward altering this natural history. Arguably the most significant development in this regard has been the periacetabular osteotomy originally described by Ganz,2 but joint-preserving approaches continue to evolve with recent evidence pointing toward greater success for these techniques when performed earlier in life. By the time degenerative joint disease is radiologically apparent, however, the opportunity for preventative measures has been lost, and salvage or reconstructive procedures are the only options. Total hip arthroplasty in patients with DDH offers unique reconstructive challenges secondary to deficient acetabular bone stock, abnormal femoral anatomy, limb-length discrepancy, abductor insufficiency, and soft tissue contractures. These patients are also typically younger, placing further demands on prostheses. Both associated abnormal anatomy and patient age have significant implications for surgical approach, implant choice, bearing surface, and long-term implant survival. Department of Orthopaedic Surgery, Mater University Hospital, Dublin, Ireland. Address reprint requests to Dr Kevin J. Mulhall, Suite 4, Sports Surgery Clinic, Santry Demesne, Dublin 9, Ireland. E-mail: [email protected]
254
1045-4527/08/$-see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2008.10.002
Classification The two most popular classification systems for developmental dysplasia are those of Crowe and Hartofilakidis and coworkers.3-5 They are both useful in surgical planning. The Hartofilakidis classification3 divides dysplasia into three categories: dysplastic hip, low dislocation, and high dislocation. It is our preferred method of classification in assessing the arthritic joint in DDH patients as, in our experience, it relates more directly to basic management decisions for acetabular reconstruction. In a “dysplastic hip” the femoral head is still contained within the original acetabulum but can be associated with segmental deficiency of the superior acetabulum and anterior wall with secondary shallowness due to medial fossa osteophyte. In “low dislocation,” the femoral head articulates in part with the true acetabulum but also with a connected false acetabulum. This type typically presents the most challenging deformities in reconstructive surgery as they are usually associated with the most severe deficiency or even absence of the superior aspect of the acetabulum. There can also be anterior and posterior segmental deficiency and the true acetabulum has a narrow opening and is shallow. With a “high dislocation,” the femoral head has migrated superiorly and posteriorly, having no contact with the true acetabulum. There is circumferential deficiency of this true acetabulum, but it is important to remember that there is often an abnormal distribution of bone stock with relative anterior wall deficiency and relative increased bone stock posteriorly.4 The Crowe and coworkers’5 classification relies on the assumption that the normal ratio of the diameter of the
Dysplasia of the hip femoral head to the height of the pelvis is 1:5 and that any proximal migration of the femoral head can be expressed either as a percentage of the height of the pelvis or of the height of the head–neck junction. It relies on the determination of four landmarks on the anteroposterior radiograph of the whole pelvis. The vertical distance of the femoral head–neck junction from the interteardrop line, which connects the lower part of the radiological teardrops, is defined as the femoral head height. Four types of dislocation of the femoral head (I to IV) are described and, while it is assumed that there is a direct relationship between the severity of the hip disease and the degree of proximal migration of the femoral head, acetabular involvement is not considered.5
Acetabular Reconstruction Anterolateral bone deficiency represents the main challenge in satisfactory reconstruction of the acetabulum. Reconstruction of the dysplastic acetabulum may be accomplished in a variety of ways that are typically predicated on the available bone stock and its distribution. In mild dysplasia it is usually possible to use a small cemented or uncemented socket placed in the native acetabulum at or near the true center of rotation. In more moderate cases, where anterior or superior bone coverage is insufficient, other options include deliberate medialization past the Kohlers line or cotyloplasty (controlled fracture of the medial acetabular wall) to gain improved lateral coverage for the socket (Fig. 1A and B). As the bony deficiency increases, use of a structural bone graft (typically the patient’s own femoral head) becomes the preferred approach. Other options that are described but that we do not employ include implantation in a high hip center posi-
Figure 1 (A and B) Acetabular reconstruction demonstrating medialization of the acetubular component used to gain increase superolateral cover. Note that the collar of the component is not seen in normal profile as it was placed in the extremely anteverted calcar segment.
255 tion (although this approach is definitely not advised for high dislocations) or use of an acetabular reinforcement ring.6 Our preferred approach is to use an uncemented cup at the anatomic hip center whenever possible. Placement of the socket at high hip center positions has several disadvantages, including the necessity for even smaller components, higher risk of impingement (and dislocation), and lack of restoration of limb length and normal hip mechanics. There is also literature to suggest that superior acetabular positioning, even without lateral displacement, leads to increased rates of loosening of both the femoral and acetabular components.7 However, others have found no relationship between the position of the cup and the rate of loosening, while others still have shown that loosening appears to depend on the amount of bony coverage obtained at the time of surgery.8 Although the precise amount of bony coverage required will depend on which acetabular prosthesis is used, most types of uncemented threaded or press-fit sockets have been reported to be successful when 20 or 30% of their surface remained uncovered or covered only with cancellous bone chips.9 In cases in which there is insufficient coverage of the acetabular component, we prefer to use structural autografting, employing the resected head appropriately contoured to create a well-contained acetabulum without excessive overhanging lateral graft. This is fixed in place to the ilium superiorly using a lag screw technique (Fig. 2A and B). Augmentation of an insufficient dysplastic acetabulum with autogenous structural bone graft has several advantages. It more commonly allows the use of a standard size of cup and allows positioning of the cup at or close to the anatomic level. The principle mechanical function of the femoral head autograft is to act as a supporting structure to the socket and to transmit load. If the autograft extends beyond the limit of the acetabular component, some degree of resorption is inevitable, because this part of the graft will not be loaded. Some authors have discouraged the use of bulk structural grafts because of a risk of graft resorption.10 However, Bobak and coworkers11 found that resorption is localized only to the lateral, unstressed part of the graft and that no femoral head graft failures occurred in their series. They reported progressive changes in the graft– host interface up to a mean of 3.5 years and they felt that a minimum of 4 years follow-up was necessary to confirm final graft fixation and incorporation. Hartofilakidis and coworkers12 compared the use of cotyloplasty, in combination with bone grafting and a cemented acetabular component, with a hemispherical cementless acetabular component. They found a significant difference in terms of survival between the two and suggested that the introduction of improved designs with a more stable locking mechanism, the use of highly cross-linked polyethylene, and the potential to use hard-on-hard bearings may lead to longer survival of the cementless components. This latter point is not new and is obviously important as accelerated polyethylene wear, presumably due to increased activity levels, has been held responsible for the higher levels of early failure and rates of osteolysis observed in younger people.13,14 Although the technique of cotyloplasty has not gained widespread use due to concerns
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Figure 2 (A and B) Use of femoral head autograft to augment deficient acetabular bone stock in Grade 2 DDH.
about the effect on residual (particularly medial bone stock) and due to results as outlined above, it may still be considered a viable alternative in selected cases.15
Femoral Reconstruction Although there are few detailed studies of the morphology of the dysplastic femur, a thorough knowledge of the altered anatomy in DDH is critical in achieving good results with reconstructive surgery. It is well known that the dysplastic hip is often associated with a narrow medullary canal and increased anteversion.16 The degree of subluxation of the hip also leads to significant alterations in the shape of the femur because of profound changes in the magnitude and direction of the joint reaction force. Since the anatomical abnormalities present are thought to increase with the severity of subluxation of the hip, the technical difficulty in performing joint replacement and the selection of an appropriate femoral prosthesis design can therefore often be related to the severity of the disease. For example, morphological analysis using computerized tomography of the femur in DDH in a Japanese population found that, as the degree of dysplasia and subluxation increases, the hip becomes gradually more anteverted, the neck shorter, and the neck–shaft angle increases.17 Very similar abnormalities have also been found in a European population.18 Similarly, other studies have shown that the dysplastic femur has a straighter, more tapered canal with a narrower medullary isthmus and a more valgus neck– shaft angle than the normal femur.19 When choosing a femoral prosthesis, particular attention must be paid to the stem characteristics, the version of the neck, and the offset so as to adequately restore abductor advantage. Adequate preoperative planning is therefore essential to ensure that appropriate implants are available for the femur in total
hip arthroplasty, a process that is facilitated by the highly modular “stem-in-sleeve” implant types. Abnormal femoral neck anteversion, previous proximal femoral osteotomies, and small femur canals with metaphyseal/diaphyseal mismatch are commonly seen in patients with DDH and are ideal indications for using a modular stem. Modularity optimizes proximal and distal implant stability while permitting adjustments to anteversion, offset, and leg length to provide custom biomechanical reconstruction of the DDH hip. Good clinical results with few complications have been reported with the use of this type of stem in complex DDH surgery.20 In cases of high dislocation, returning the center of rotation to the anatomic hip center will be accompanied by limb lengthening (Fig. 3A and B). When this is predicted to be at or greater than 3 cm it is wise to plan for a shortening osteotomy to avoid overlengthening with resultant excess tension on the neurovascular structures and the femoral and sciatic nerves in particular. Different techniques are described, but our preferred approach is to perform a subtrochanteric osteotomy. We prepare the metaphyseal segment first for the appropriately sized modular collar or sleeve and prepare the canal for a well-fitting stem. The osteotomy then is performed and the length of the appropriate shortening segment is determined by reducing the proximal fragment, with trial implants in place, and directly measuring the length of femur that needs to be resected to get a stable appropriate length construct. With a well-fitting stem the torsional stability of the fluted modular stem gives excellent fixation of the subtrochanteric osteotomy alone, but we often supplement the osteotomy site with a strut derived from the resected femur (Fig. 3C). Although modular constructs have gained increasing popularity for these complex reconstructions there are a wide variety of implants that have been and continue to be used.
Dysplasia of the hip
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Figure 3 (A-C) Anteroposterior radiograph and computed tomography reconstruction views of High/Grade 3 dislocation, demonstrating pseudoacetabulum in typical posterosuperior location. A subtrochanteric osteotomy allows restoration of the anatomical hip center in the true acetabulum without excessive leg lengthening. A strut of resected femur was replanted with cerclage cables at the osteotomy site. Because of extremely small true acetabular dimensions it was decided to use a cemented highly cross-linked polyethylene cup and obtain maximum polyethylene thickness rather than our standard approach of using an uncemented cup.
Reconstructing appropriate version limits the usefulness of many metaphyseal fixed uncemented components in moderate or severe cases in which the native femur is very anteverted. Cemented components can avoid this drawback by allowing a downsized stem to be placed in the correct version. Resurfacing arthroplasty has gained popularity worldwide and has been described for use in DDH. One of the continued advantages of resurfacing is the preservation of femoral bone stock for future possible revisions; however, other previous potential advantages of hard and large diameter bearings are increasingly also offered by other modular uncemented implants. The Birmingham resurfacing implant has a specific “dysplasia” cup that allows supplementary screw fixation if deemed necessary and medium-term results with this implant in all grades of developmental dysplasia have been acceptable, albeit worse than in matched patients with osteoarthritis treated in the same manner. McBryde and coworkers21 found a significant difference in survival, with 5.2% of patients with dysplasia requiring revision compared with 0% of those with osteoarthritis. However, there was no difference in Oxford hip score between those two groups. Other studies have also reported inferior results for resurfacing in DDH in comparison with patients with other condi-
tions, with, notably, acetabular failures being more prevalent than failures on the femoral side.22
Outcomes of Total Hip Arthroplasty in DDH The use of bulk structural autologous graft from the femoral head to augment the superolateral aspect of the acetabular rim was initially proposed by Harris.23 Although the shortterm clinical results of this technique were excellent, the failure rate after approximately 12 years was high (46%). This may be related to the complex pathoanatomy encountered at the level of the true acetabulum and the abnormal distribution of stresses combined with the unfavourable long-term biological behavior of structural grafts.24 Others have demonstrated a 20% revision rate and a 46% rate of radiological failure at a mean follow-up of 11.8 years.10 However, descriptions of THA for Grade 2 or 3 DDH without the use of autograft have been very poor, with rates of failure between 16 and 59% after follow up for 8.5 to 16 years.8 Various authors have reported on the use of total hip arthroplasty in younger patients. Kim and coworkers25 re-
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258 ported on 10-year follow-up of cementless prostheses in patients less than 50 years of age. They found a survival rate of 99%, with no case occurring because of aseptic loosening. They reported a thigh pain rate of 10%, with all resolving by 2 years. Dudkiewicz and coworkers26 showed poorer survival in patients less than 30 years with predominately cementless implants. This small series had a revision for any reason rate of almost 50%. One group found excellent clinical results with Charnley low friction arthroplasty with up to 15 years follow-up. They emphasized preoperative assessment, adequate exposure, availability and selection of instruments and components, correct placement of components, and attention to detail at every stage are the most important aspects of the procedure.11 In a series of Birmingham hip resurfacings it was found that younger patients had a significantly worse outcome in terms of Oxford hip score and slightly worse survival than older patients, with the authors claiming this was due to secondary causes of osteoarthritis such as DDH, which represented 10% of their study population.27 The medium-term clinical results of other surface arthroplasties in patients with Crow type I or II DDH have also failed to meet initial expectations, with a 10% conversion rate to total hip arthroplasty due to impingement, femoral component loosening, or femoral neck fracture.28 The risk factors for femoral neck fracture in hip resurfacing for developmental dysplasia, as determined by retrieval studies, included poor bone quality with large cysts and inadequate component seating.29
Complications and Revision Most of the complications typically associated with arthroplasty in DDH are related to the degree of abnormal anatomy. Patients with unilateral high dislocations have substantial limb-length discrepancies and limps. Recent clinical studies have shown excellent results when good primary stability is achieved and the joint is restored to the anatomic hip center.30 However, restoring the normal hip center is complicated by not just bone stock issues but also soft tissue contractures. The rate of nerve palsies is higher after total hip arthroplasty in patients with hip dysplasia, and this has been commonly attributed to stretching of the nerves during lengthening.31 The exact amount of distraction that will cause sciatic nerve dysfunction is not known, but acute lengthening of ⬎2 to 4 cm has been associated with an increased risk of nerve injury.32 However, in a 1999 report on eight nerve palsies after 508 total hip arthroplasties, Eggli and coworkers33 indicated that the palsies were not related to the amount of lengthening per se but to the difficulty of the surgery. There were no clinically evident femoral or sciatic nerve palsies in one series of patients with Crowe IV dysplasia treated with total hip arthroplasty.34 As mentioned earlier, if we predict 3 cm or greater lengthening, our preferred method of controlling length is by a subtrochanteric osteotomy. In our experience this has not been associated with any complications but there is the possibility of delayed or nonunion at the osteotomy site.
Figure 4 (A-C) A patient with cerebral palsy and spastic diplegia with progressive subluxation despite osteotomies of femur and pelvis. Because of intrinsic stability issues in this patient a constrained acetabular implant was employed.
Dysplasia of the hip The rate of dislocation after total hip arthroplasty in these cases has been reported to be as high as 5 to 11%. This is related to the complexities of femoral and acetabular version, soft tissue tension, length, and small component size and emphasizes the importance of a sound knowledge of the individual anatomy in placing components accurately and of performing meticulous intraoperative assessment of stability (Fig. 4A and B). As most of these patients are younger and more active, the main long-term issues remain wear, osteolysis, and failure. There have been many developments in bearings and materials in recent times and it is hoped these will improve implant survivorship for these patients. There are ongoing concerns regarding metal-on-metal bearings in all patient groups, but particularly in women of child-bearing age because of concerns that associated ion levels may cause birth defects. Although there is no clinical evidence demonstrating an increased incidence of cancer or birth defects with metalon-metal bearings, many surgeons are using highly crosslinked polyethylene with larger diameter heads or ceramic bearings in these patients with good results to date compared with traditional polyethylene bearings.13,35-37 Revision total hip arthroplasty in patients with a previous diagnosis of DDH can also be a challenging and technically demanding procedure. Two major concerns are deficient acetabular bone stock and the position of the acetabular implant, particularly if the center of the hip has not been restored in the primary procedure. While some advocate the use of a high hip center to take advantage of remaining bone stock and to avoid the use of a structural graft,38 this does not contribute to the correction of limb-length discrepancy, does not provide good bone stock for revision surgery, and is associated with early acetabular loosening and a higher rate of ischial impingement.7 The pattern of bone loss in DDH, a reduced anteroposterior diameter combined with poor superior support, may be further increased by surgical bone loss from the primary operation, migration of the cup, and particle-induced osteolysis. Anatomical placement of the acetabular component should be the goal in revision THA. However, it is sometimes impossible to achieve adequate contact between the host one and the implant because of severe and progressive bone destruction after the primary procedure. Such bone loss can be managed by the use of structural allograft bone, by impaction grafting over suitably fixed mesh and a cemented cup, by proximal placement of the cup, or by using uncemented implants such as oblong, trabecular metal or jumbo cups or customized implants.39,40 The choice of approach here obviously depends to an extent on availability and experience, but it is worth noting that high cup placement in revision surgery in these cases has been associated with loosening of the acetabular component in 41% at 2 and 5 years.
Conclusion In summary, patients with DDH present a unique set of reconstructive problems based on abnormal femoral and acetabular anatomy. They also develop degenerative joint dis-
259 ease requiring arthroplasty at a relatively young age with associated implications for outcomes and implant survivorship. Despite these considerations, once appropriate techniques and implants are used, there is good evidence to show excellent symptomatic relief and improved quality of life with acceptable survivorship after total hip arthroplasty for DDH.
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260 21. McBryde CW, Shears E, O’Hara JN, et al: Metal-on-metal hip resurfacing in developmental dysplasia: A case-control study. J Bone Joint Surg Br 90:708-714, 2008 22. Davlin LB, Amstutz HC, Tooke SM, et al: Treatment of osteoarthrosis secondary to congenital dislocation of the hip: Primary cemented surface replacement compared with conventional total hip replacement. J Bone Joint Surg Am 72:1035-1042, 1990 23. Harris WH, Crothers O, Oh I: Total hip replacement and femoral-head bone-grafting for severe acetabular deficiency in adults. J Bone Joint Surg Am 59:752-759, 1977 24. Goldberg VM: The biology of bone grafts. Orthopedics 26:923-924, 2003 25. Kim YH, Oh SH, Kim JS: Primary total hip arthroplasty with a secondgeneration cementless total hip prosthesis in patients younger than fifty years of age. J Bone Joint Surg Am 85:109-114, 2003 26. Dudkiewicz I, Salai M, Ganel A, et al: Total hip arthroplasty in patients younger than 30 years of age following developmental dysplasia of hip (DDH) in infancy. Arch Orthop Trauma Surg 122:139-142, 2002 27. Steffen RT, Pandit HP, Palan J, et al: The five-year results of the Birmingham Hip Resurfacing arthroplasty: An independent series. J Bone Joint Surg Br 90:436-441, 2008 28. Amstutz HC, Antoniades JT, Le Duff MJ: Results of metal-on-metal hybrid hip resurfacing for Crowe type-I and II developmental dysplasia. J Bone Joint Surg Am 89:339-346, 2007 29. Amstutz HC, Campbell PA, Le Duff MJ: Fracture of the neck of the femur after surface arthroplasty of the hip. J Bone Joint Surg Am 86: 1874-1877, 2004 30. Perka C, Fischer U, Taylor WR, et al: Developmental hip dysplasia treated with total hip arthroplasty with a straight stem and a threaded cup. J Bone Joint Surg Am 86:312-319, 2004
J. Cashman and K.J. Mulhall 31. Schmalzried TP, Amstutz HC, Dorey FJ: Nerve palsy associated with total hip replacement: Risk factors and prognosis. J Bone Joint Surg Am 73:1074-1080, 1991 32. Lewallen DG: Neurovascular injury associated with hip arthroplasty. Instr Course Lect 47:275-283, 1998 33. Eggli S, Hankemayer S, Muller ME: Nerve palsy after leg lengthening in total replacement arthroplasty for developmental dysplasia of the hip. J Bone Joint Surg Br 81:843-845, 1999 34. Lai KA, Shen WJ, Huang LW, et al: Cementless total hip arthroplasty and limb-length equalization in patients with unilateral Crowe type-IV hip dislocation. J Bone Joint Surg Am 87:339-345, 2005 35. Brodner W, Grohs JG, Bancher-Todesca D, et al: Does the placenta inhibit the passage of chromium and cobalt after metal-on-metal total hip arthroplasty? J Arthroplasty 19:102-106, 2004 36. Bizot P, Hannouche D, Nizard R, et al: Hybrid alumina total hip arthroplasty using a press-fit metal-backed socket in patients younger than 55 years: A six- to 11-year evaluation. J Bone Joint Surg Br 86:190-194, 2004 37. Riska EB: Ceramic endoprosthesis in total hip arthroplasty. Clin Orthop Relat Res 297:87-94, 1993 38. Russotti GM, Harris WH: Proximal placement of the acetabular component in total hip arthroplasty: A long-term follow-up study. J Bone Joint Surg Am 73:587-592, 1991 39. Tanzer M: Role and results of the high hip center. Orthop Clin North Am 29:241-247, 1998 40. Perka C, Schneider F, Labs K: Revision acetabular arthroplasty using a pedestal cup in patients with previous congenital dislocation of the hip: Four case reports and review of treatment. Arch Orthop Trauma Surg 122:237-240, 2002